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  <title>Module: ActionController::Caching::Sweeping</title>
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          <td><strong>Module</strong></td>
          <td class="class-name-in-header">ActionController::Caching::Sweeping</td>
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            <td><strong>In:</strong></td>
            <td>
                <a href="../../../files/vendor/rails/actionpack/lib/action_controller/caching/sweeping_rb.html">
                vendor/rails/actionpack/lib/action_controller/caching/sweeping.rb
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      <p>
Sweepers are the terminators of the caching world and responsible for
expiring caches when model objects change. They do this by being
half-observers, half-filters and implementing callbacks for both roles. A
Sweeper example:
</p>
<pre>
  class ListSweeper &lt; ActionController::Caching::Sweeper
    observe List, Item

    def after_save(record)
      list = record.is_a?(List) ? record : record.list
      expire_page(:controller =&gt; &quot;lists&quot;, :action =&gt; %w( show public feed ), :id =&gt; list.id)
      expire_action(:controller =&gt; &quot;lists&quot;, :action =&gt; &quot;all&quot;)
      list.shares.each { |share| expire_page(:controller =&gt; &quot;lists&quot;, :action =&gt; &quot;show&quot;, :id =&gt; share.url_key) }
    end
  end
</pre>
<p>
The sweeper is assigned in the controllers that wish to have its job
performed using the <tt>cache_sweeper</tt> class method:
</p>
<pre>
  class ListsController &lt; ApplicationController
    caches_action :index, :show, :public, :feed
    cache_sweeper :list_sweeper, :only =&gt; [ :edit, :destroy, :share ]
  end
</pre>
<p>
In the example above, four actions are cached and three actions are
responsible for expiring those caches.
</p>
<p>
You can also name an explicit class in the declaration of a sweeper, which
is needed if the sweeper is in a module:
</p>
<pre>
  class ListsController &lt; ApplicationController
    caches_action :index, :show, :public, :feed
    cache_sweeper OpenBar::Sweeper, :only =&gt; [ :edit, :destroy, :share ]
  end
</pre>

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